Material handlers include a frame, a front axle, a rear axle, and front and rear wheels. Typically, the front axle is either fixed relative to the frame or pivotal about a horizontal axis that extends centrally along the length of the frame. The rear axle is pivotally coupled to the rear end of the frame. The rear axle is allowed to freely pivot about the horizontal axis and thereby tilt in response to changes in ground contours in order to provide the vehicle with increased comfort and stability. However, under various loading conditions, the freely pivoting rear axle may cause the material handler to become less stable. As a result, some material handlers include rear axle stabilizer systems that have one or more lockable cylinders connected to a vehicle hydraulic system and positioned between the frame and the rear axle. The cylinders are generally open to allow the cylinder and the rear axle to move freely. The cylinders are also lockable to rigidly fix the position of the rear axle relative to the frame.
Material handlers also include telescoping booms which are used to lift and transport loads. A typical telescoping boom includes a rearward or lower end that is coupled to a back end of the frame and a forward or upper end that extends toward a front end of the frame. The telescoping boom is extendable between a retracted position and an extended position and pivotable between a lowered position and a raised position. The telescoping boom is typically equipped with a fork that is insertable underneath a pallet in order to raise a load that is stacked on top of the pallet and move it to another position. The load is moved relative to the material handler and therefore it is possible to locate the load into a position that will cause the material handler to become unbalanced and, in extreme circumstances, cause the material handler to tip over.
In order to alert the operator to a potential unbalanced condition, some material handlers include a tip over warning system to alert a vehicle operator of the amount of longitudinal weight shift from rear to front of the vehicle. One or more strain gauges are located on the rear axle to sense the vehicle weight supported by the axle. The signals from the strain gauges are used to determine the remaining weight on the rear axle of the vehicle. The system activates a warning lamp or buzzer that indicates to the operator that a longitudinal tip over may soon occur.
Other material handlers, especially cranes, include systems that measure the carried load and calculate the center of gravity of the machine and load by measuring the machine geometry. Typically, these systems measure the angle, length, and orientation of the boom. For the method to work properly, the machine must be level and stationary. These systems activate warning alarms to warn the operator that the vehicle is potentially unstable.